An intermediate in the synthesis of the plant hormone ethylene; acts as a partial agonist at the glycine-binding site on NMDA receptors (EC50 = 0.7-0.9 μM) and, in the presence of high levels of glutamate, as a competitive antagonist at the glutamate-binding site on NMDA receptors (EC50 = 81.6 nM); protects against neuron cell death in in vivo models of ischemia